1996 Polaris SLT780 compression issues

[Rookie 101]

1996 Polaris SLT780. It shows 37 hours on it. I T had sat in a barn for a few yrs prior to me purchasing it. I ran it in lake but had to use the choke to get it up to full speed. I decided to rebuild the carburetors. After reassembling and running in lake I have no compression in one cylinder. I didn't check prior to rebuilding carbs if I did. What could be the issue??

 

[racerone]

Hole in a piston is a possibility.----If it is a 4 stroke it could be a valve stuck open.

 

[QBhoy]

If this is the old 2 stroke motor I think it is…it may have had an issue with a power valve causing damage, if that’s possible, the way it is on more familiar Yamaha engines of similar type. If you have absolutely zero compression…for sure, some very serious is going on…like total failure of the piston or similar on the top end. Better news might be a head failure…perhaps from ingesting water or the wrong starting procedure on the hose. Or perhaps if she was towed too fast without the engine running perhaps. Not common and odds on is the worst case, I’m afraid. Let us know how you get on…or if you mean that compression is not an absolute zero

 

[Scott Danforth]

1996 Polaris SLT780. It shows 37 hours on it. I T had sat in a barn for a few yrs prior to me purchasing it. I ran it in lake but had to use the choke to get it up to full speed. I decided to rebuild the carburetors. After reassembling and running in lake I have no compression in one cylinder. I didn't check prior to rebuilding carbs if I did. What could be the issue??

Running with a choke meant something in one of the carbs was plugged

Running it like you did with the choke on probably killed one of the bores.

 

[QBhoy]

Running with a choke meant something in one of the carbs was plugged

Running it like you did with the choke on probably killed one of the bores.

Fair point and a possibility for sure be keen to hear if it actually shows absolute zero compression. Might tell a story